The present invention relates to a separate lubricating system best adapted for use in a crankcase compression type lubricating system in a two-stroke-cycle engine (hereinafter referred to as a "two cycle engine") suitable for use in, for instance, an outboard marine engine unit.
In the conventional outboard engine having a separate lubricating system, lubricating oil is supplied from an oil tank with an air breather to a plunger pump driven by the crankshaft of a two cycle engine and is thus forced to flow toward parts of the two cycle engine to be lubricated (hereinafter referred to as "the lubricated parts").
However, when the outboard engine is tilted up, the attitude of the outboard engine greatly changes as a whole, so that air may be swept into and entrapped within the plunger pump. Therefore a problem arises in that the quantity of the lubricating oil delivered from the plunger pump cannot be metered correctly, and consequently the engine cannot be satisfactorily lubricated.
Especially in the case of a plunger pump disposed above the oil tank, once the air has been aspirated into the plunger pump, it becomes more difficult to discharge the entrapped air, so that the above-described problems are further aggravated.